The present invention relates to a apparatus and method for using a vacuum chuck to assure adhesion of a planar substrate, while using electrodes to attract grains (e.g., dry powder) to adhere to the planar substrate. The electrodes may also participate in holding the planar substrate.
In the field of semiconductor processing, semiconductor wafers have been held in place for processing with clamps, magnetic clamps, electrostatic chucks and vacuum chucks. Such semiconductor processing typically seeks to direct mask material, mask developing materials such as photoresist, dopant and etchant to the semiconductor. In directing etchant to the semiconductor, electromagnetic fields may be used to direct the majority of etching to occur in a given direction; such directed etching processes were not intended to coat the semiconductor with grains. For example, Weeks et al., U.S. Pat. No. 5,692,873, McKinley et al., U.S. Pat. No. 5,724,121 and Hasegawa et al., U.S. Pat. No. 5,676,758 all describe vacuum chucks in connection with various semiconductor apparatuses, and also mention that electrostatic chucks can also be used to clamp the semiconductor wafer. A Di Milia et al. patent, U.S. Pat. No. 4,551,192, describes a pinchuck that can be used to hold a substrate during a lithography process using vacuum or electrostatic forces.
Electrostatic chucks can be used to direct grains of material to a substrate to provide a coated substrate. Various methods can be used to assure that such coating techniques apply an accurate and, in some cases, spatially resolved, coating of material, making it feasible to use electrostatic coating technology to apply pharmaceuticals. xe2x80x9cSpatially resolvedxe2x80x9d refers to depositions at defined subregions of a surface. Examples of technology in this area include Sun, xe2x80x9cChucks and Methods for Positioning Multiple Objects on a Substrate,xe2x80x9d U.S. Pat. No. 5,788,814, issued Aug. 4, 1998; Sun et al., xe2x80x9cElectrostatic Chucks,xe2x80x9d U.S. Pat. No. 5,858,099, issued Jan. 12, 1999; Pletcher et al., xe2x80x9cMethod and Apparatus for Electrostatically Depositing a Medicament Powder Upon Predefined Regions of a Substrate,xe2x80x9d U.S. Pat. No. 6,007,630, issued Dec. 28, 1999; and Sun et al., xe2x80x9cAcoustic Dispenser,xe2x80x9d U.S. Pat. No. 5,753,302, issued May 19, 1998. These documents are incorporated by reference herein in their entirety.
In the course of testing such accurate deposition apparatuses to coat flexible planar substrates, applicant has discovered that while the electrostatic chuck can be used to hold the planar substrate and direct the electrostatic deposition of grains, a combination further using vacuum forces on the chuck increases the processing efficiency such that the planar substrate more reproducibly becomes adhered without deformations and air pockets. Such a combination preferably takes the form of a vacuum chuck onto which is layered a thin, e.g., about 25 xcexcm to about 250 xcexcm thick electrostatic chuck having holes through which the vacuum is communicated to the planar substrate.
In one embodiment, the invention relates to an apparatus for electrostatically adhering grains to a planar substrate comprising:
a. an electrostatic chuck having a collection surface with at least one grain collection zone for, when the planar substrate is layered on the collection surface, electrostatically directing charged grains to a corresponding surface on the planar substrate; and
b. a pattern of holes through the electrostatic chuck allowing a source of low pressure to act through the electrostatic chuck to adhere the planar substrate.
The apparatus can further comprise:
c. a low pressure chuck having an adhesion surface having a plurality of holes for aligning with the holes to connect the holes to the source of low pressure.
The adhesion surface can be a porous material.
In one embodiment, the electrostatic chuck comprises (i) the collection surface, (ii) a dielectric layer located behind the collection surface, (iii), behind the dielectric layer, one or more attraction electrodes for attracting grains to the collection zones. Also, the electrostatic chuck can further comprises (iv) one or more shield electrodes for discouraging charged grains from being directed away from the collection zones. A rotatable cluster of a plurality of said low pressure chucks can be used, where the low pressure chucks rotate to repeatedly and sequentially present the adhesion surfaces to the charged grain dispenser. A low pressure control mechanism can be operated to sequentially apply low pressure to low pressure chucks and sequentially releasing the low pressure from low pressure chucks such that there is a contiguous collection of the low pressure chucks to which low pressure is applied and a contiguous collection of the low pressure chucks with no applied low pressure, thereby allowing a sheet of planar substrate to be presented to the charged grain dispenser while adhered to an electrostatic chuck and low pressure chuck and then released for further processing.
Also provided is an electrostatic deposition apparatus for electrostatically depositing grains onto a planar substrate comprising:
i. at least one low pressure chuck having an adhesion surface having a plurality of holes for conveying low pressure to the adhesion surface;
ii. layered on the collection surface, at least one electrostatic chuck having a collection surface with at least one grain collection zone for, when the planar substrate is layered on the collection surface, electrostatically directing charged grains to a corresponding surface on the planar substrate, the at least one electrostatic chuck having a pattern of holes through the electrostatic chuck allowing the low pressure to act through the electrostatic chuck to adhere the planar substrate; and
iii. a charged grain dispenser for directing charged grains towards the grain collection zones.
Still further provided is a method of electrostatically applying a grains to a planar substrate comprising:
a. adhering the planar substrate to an electrostatic chuck with a pressure differential conveyed to the planar substrate via passages through the electrostatic chuck;
b. applying a voltage to the electrostatic chuck to attract charged grains to at least one grain collection zone defined by the electrostatic chuck;
c. directing charged grains towards the charged grain collection zone; and
d. electrostatically adhering charged grains on a portion of the planar substrate corresponding to the grain collection zone.